docs: def get_connection_pool(self, pool_id, *args, **kwargs):
          """get a connection pool, transparently creating it if it doesn't already exist
  
          :Parameters:
              - `pool_id`: unique id for a connection pool
          """
          assert isinstance(pool_id, (str, unicode))
          if not hasattr(self, '_pools'):
              self._pools = {}
          if pool_id not in self._pools:
              self._pools[pool_id] = ConnectionPool(*args, **kwargs)
          # logging.debug("%s: _connections = %d", pool_id, self._pools[pool_id]._connections)
          return self._pools[pool_id]